Containers are commonly used in the food industry for transporting food home by a consumer, especially in the ready-to-eat food industry and in the restaurant industry for packaging leftovers. Hinged or clamshell food containers are very convenient in that they comprise a cover that is hingedly mounted to a tray, which provides for convenient storage by the food service provider and convenient operation by the user.
Clam shell containers are generally thermoformed from either expanded thermoplastics (foamed plastics), such as expanded polystyrene, or non-expanded thermoplastics (sheet plastics), sheet plastics, such as polypropylene (PP), oriented polystyrene (OPS) or polyethylene terephthalate (PET). Containers made from the foamed plastics have better insulating properties compared to the sheet plastics. Containers made from sheet plastics may have sharper corners, greater strength and more tear resistance compared to foamed plastics. The foam containers are best suited for applications where the insulating characteristics of the foam are of a high priority, such as when the food is to be maintained at temperature prior to serving. The non-expanded thermoplastic containers are best suited when forming an interlocking seal, as compared to an abutting seal, between the cover and the tray to prevent leakage is a high priority, such as when leftovers are being taken home from a restaurant. The non-expanded materials are much more suitable than the expanded materials for being easily formed into the cooperating complex shapes necessary for the cover and the tray to form a leak-proof seal when closed.
The use of interlocking seals, while beneficial to prevent leakage, are sufficiently air-tight that, for hot foods, there is a need to provide a vent to provide for the escape of air heated by the hot foods.